1. Field of the Invention
The invention relates to the use on a machine of a non extendible flexible or articulated band of a transmission or travelling system and it relates more particularly to a device ensuring the permanent tension of such a flexible or articulated band, in particular a caterpillar track.
2. Description of the Prior Art
Tensioning devices are known for flexible belts, which comprise a roller designed to engage the belt and which is movable in the plane of the latter. Such tensioning devices are however not applicable for tensioning flexible or articulated tracks in the longitudinal direction equipping different machines and, in particular, the flexible elastomer material tracks equipping the tired wheels of an argicultural tractor.
In fact, in this application, the roller of the tensioning device would be formed by a wheel whose axle would then be carried rigidly by the chassis of the machine which, when the path over which the machine is travelling is not perfectly flat, would prevent the normal movement thereof and would cause damage thereto.
Half-track devices are also known, for example from the U.S. Pat. No. 2,719,062, for tractors in which the structural assembly supporting the tensioning wheels of the track is fixed floatingly at the level of the axle of the driving wheel of the tractor. These devices have different drawbacks such as:
1. A lack of rigidity in the horizontal plane, resulting in poor guidance of the band and considerable risks of the tracks coming off, particularly in bends;
2. The impossibility of correctly and finally adjusting, whatever the conditions of use, the geometry of the tensioning wheels which takes three parameters into account:
the alignment, i.e. the coincidence of the longitudinal axis of the driving wheel with that of the tensioning wheels, PA0 the set of the axle pin, by slanting the tensioning wheels with respect to the longitudinal vertical plane, PA0 the toe-in, by pivoting the tensioning wheels about a vertical axis so as to adjust their front part inwardly.
These three parameters are essential for obtaining correct guidance of the band under all circumstances, in particular when it is a questionof a friction driven band.
3. The transmission of a high force, amplified by the lever arm represented by the length of the floating structure, at the level of the axle casing of the drive wheel, adversely affecting the resistance thereof and making the neighboring mechanical assemblies fragile.
The use of a tensioning device is necessary for example on half track machines such as agricultural tractors in which, with the flexible elastomer material caterpillar track mounted on tired wheels, good friction transmission of the drive force to the track as well as correct load-carrying ability of the track are permanently conditioned by correct tension of the latter.